Japanese Utility Model Laid-Open Publication No. 06-17055 discloses a switch device in which a button is pushed down or the pushed button is released to switch an electrical contact state between a movable contact point and a fixed contact point.
FIGS. 7 A to 7C are views explaining a switch device 500 according to a conventional example. FIG. 7A is a sectional view illustrating a state before wear of contact points and pushing down a button. FIG. 7B is an enlarged view of an area A in FIG. 7A illustrating a state having pushed down a button and before wear of contact points. FIG. 7C is an enlarged view of an area A in FIG. 7A illustrating a state having pushed down a button and after wear of contact points.
In the switch device 500, metallic movable contact points 530 provided on one end side of a button unit 520 and metallic fixed contact points 540 provided in a bottom wall 511 of a case member 510 are arranged to face to each other in a contact point accommodation chamber S of the case member 510 (refer to FIG. 7A).
The button unit 520 is urged in a direction of being away from the fixed contact points 540 along a center axis X1 of the button unit 520 by a spring member 550. When an operating button 522 provided on the other end side of the button unit 520 is pushed down against an elastic force of the spring member 550, the movable contact points 530 make contact with the fixed contact points 540 (switch-on) or when the pushed operating button 522 is released, the movable contact points 530 are disconnected from the fixed contact points 540 by the elastic force of the spring member 550 (switch-off).
Here, the metallic fixed contact point 540 is worn away due to arc electric discharge generated between contact points for every time of switching on/off or due to contact with the movable contact point 530. The switch device 500 is provided with stoppers 512 to prevent a state where when the amount of wear of the fixed contact point exceeds a predetermined value, the movable contact point and the fixed contact point adhere to each other, which causes a large current to continue to flow therebetween.
That is, the switch device 500 is provided with the plastic stopper 512 in a position closer to the center axis X1 than the fixed contact point 540 on the bottom wall 511 of the case member 510.
When the amount of wear of the fixed contact point is equal to or less than the predetermined value, a gap L1 between the fixed contact point 540 and the movable contact point 530 is set to be narrower than a gap L2 between the stopper 512 and the movable contact point 530. Therefore upon pushing down the operating button 522, the movable contact point 530 makes contact with the fixed contact point 540 prior to making contact with the stopper 12 to switch on (refer to FIG. 7B).
When the gap L1 between the fixed contact point 540 and the movable contact point 530 becomes approximately equal to the gap L2 between the stopper 512 and the movable contact point 530 as a result of the wear of the fixed contact point 540, the movable contact point 530 abuts on the plastic stopper 512 to stop.
Since the movable contact point 530 makes contact with the fixed contact point 540 as well in this state (refer to FIG. 7C), it is difficult to prevent the state where the movable contact point 530 and the fixed contact point 540 adhere to each other, which causes a large current to continue to flow therebetween.
Therefore, when the amount of wear of the fixed contact point exceeds the predetermined value, it is required that the movable contact point does not make contact with the fixed contact point certainly.